A combustion space with a high level of thermal and/or thermo-mechanical loading such as for example a furnace, a hot gas duct or a combustion chamber in a gas turbine, in which space a hot medium is produced and/or ducted, is provided with a suitable lining as protection against excessive thermal stressing. The lining usually consists of a heat-resistant material and protects a wall of the combustion space from direct contact with the hot medium and the high level of thermal loading associated therewith.
U.S. Pat. No. 4,840,131 relates to a securing of ceramic lining elements to a wall of a furnace. Here a system of rails secured to the wall and having a plurality of ceramic rail elements is provided. The rail system allows the lining elements to be supported on the wall. Further ceramic elements can be provided between a lining element and the wall of the furnace, including a layer of loose, partially compressed ceramic fibers, this layer having at least roughly the same thickness as the ceramic lining elements or a greater thickness. The lining elements here are rectangular in shape with a planar surface and consist of a heat-insulating, fireproof, ceramic fibrous material.
U.S. Pat. No. 4,835,831 relates likewise to the affixing of a fireproof lining to a furnace wall, in particular a vertically disposed wall. A layer consisting of glass, ceramic, or mineral fibers is affixed to the metal wall of the furnace. Said layer is affixed to the wall by means of metal brackets or by adhesive means. Wire netting having honeycomb type mesh is affixed to said layer. The meshed netting serves also to prevent the ceramic-fiber layer from dropping down. An even, closed surface of fireproof material is additionally applied to the layer thus secured by means of a suitable spraying method. The described method largely prevents the rebounding of fireproof particles formed during spraying, as would occur were the fireproof particles sprayed onto the metal wall directly.
A ceramic lining of the walls of thermally highly stressed combustion spaces, for example of gas turbine combustion chambers, is described in EP 0 724 116 A2. The lining consists of wall elements made of high-temperature resistant structural ceramic material, such as silicon carbide (SiC) or silicon nitride (Si3N4) for example. The wall elements are secured mechanically by means of a central securing bolt and resiliently to a metal support structure (wall) of the combustion chamber. A thick thermal insulation layer is provided between the wall element and the wall of the combustion space, so that the wall element is correspondingly distanced from the wall of the combustion chamber. The insulation layer, which is about three times as thick as the wall element, consists of a ceramic fibrous material prefabricated in blocks. The dimensions and external shape of the wall elements can be tailored to the geometry of the space to be lined.
Another kind of lining for a combustion space with a high level of thermal loading is described in EP 0 419 487 B1. The lining consists of heat shield elements secured mechanically to a metal wall of the combustion space. The heat shield elements are in direct contact with the metal wall. To avoid excessive heating of the wall resulting for example from a direct transfer of heat from the heat shield element or the ingress of hot medium into the gaps formed by the mutually adjacent heat shield elements, the space formed by the wall of the combustion space and the heat shield element is exposed to cooling air, so-called barrier air. The barrier air prevents hot medium from penetrating as far as the wall and simultaneously cools the wall and the heat shield element.
WO 99/47874 relates to a wall segment for a combustion space and to a combustion space of a gas turbine. Described therein is a wall segment for a combustion space, which can be exposed to a hot fluid, for example a hot gas, having a metal support structure and a heat protection element secured to the metal support structure. A deformable separating layer is inserted between the metal support structure and the heat protection element, its purpose being to absorb and compensate to a significant degree for possible relative movements of the heat protection element and the support structure. Such relative movements can be caused for example in the combustion chamber of a gas turbine, in particular an annular combustion chamber, by the materials used having different thermal expansion responses or by pulsations in the combustion space that can occur in the event of irregular combustion to produce the hot working medium or as a result of resonant effects. At the same time the separating layer causes the relatively inelastic heat protection element generally to lie flatter on the separating layer and metal support structure, since the heat protection element penetrates partially into the separating layer. The separating layer can thus also compensate for irregularities resulting during production on the support structure and/or heat protection element, which can result locally in an unfavorable force input.
If the surface of a heat shield element is suddenly exposed to a hot medium, for example a hot gas from a combustion system, its temperature rises rapidly in a short time. The resulting relative thermal expansions produce thermally induced stresses, which can lead either immediately or after a certain number of stress or load cycles to cracks occurring in the material of the heat shield element, as a result of which the heat shield element may fail. Depending on the presence of other loads, such as vibrations or chemical effects, the effect of the damage can be further reinforced, so that the useful life of the heat shield element is limited by crack formation. Heat shield elements must therefore, particularly in combustion chambers of gas turbine installations, be examined regularly for cracks with reports being produced and must be replaced at regular intervals to ensure operational safety.
The invention is based on the observation that ceramic heat shield elements in particular, due to their necessary flexibility in respect of thermal expansion, are frequently only protected inadequately from the thermo-mechanical loading that occurs, in particular due to temperature change loading.